The currently available and established methods for water purification do not have the capability of removing organic pollutants at the level of a few parts per billion (ppb). In contrast to the inorganic metal ions, the organic pollutants do not bind to the polymeric resins and do not solidify to mineral materials. The conventional methods of water purification employ either filtration through active carbon or reverse osmosis. Active carbon removes organic compounds, it however fails to remove a large number of organic pollutants at the level of a few ppb. Other materials such as zeolites have well-defined permeability but have little affinity to the organic compounds present in water. In addition active carbon and zeolites absorb moisture and therefore they are not effective in water. On the other hand, although reverse osmosis has been successfully used for the desalination of water, operation at high pressures is required, usually 20-100 bar, and as a consequence large energy consumption is required for achieving effective separation. It is also impossible to achieve 100% water recovery because pressure increases as more water is forced to pass through the dense membrane. For this reason the continuation of separation procedure becomes non-practical. In addition reverse osmosis cannot remove all small molecules from water because the membrane is not completely semipermeable. As a result a small concentration of organic molecules usually leaks to the purified water. More effective for water purification from organic pollutants is the preparation of modified lipophilic polymers bearing nanocavities and their application for encapsulating organic pollutants.
By now, known cases for the preparation of certain lipophilic polymers and their application for encapsulating organic compounds contained in water refer to modified cyclodextrin derivatives as described in the article entitled “New Organic Nanoporous Polymers and their Inclusion Complexes”, Chem. Mater. 1999, 11, 872-874, among others. The disadvantage of these known modified polymers is that their nanocavities have in each case specific size and shape, which cannot be modified. The consequence of this disadvantage is that only specific organic pollutants can be encapsulated in specific cyclodextrin derivatives. Particularly, the molecule of the organic compound must in every case be smaller than or almost of similar size to the nanocavity of the cyclodextrin polymer and its shape should match to that of the cavity, in order that it is encapsulated and consequently that water purification is achieved. The result is that organic molecules that are large-sized or of irregular shape cannot be encapsulated into the cavities of any kind of cyclodextrin's. In order for water purification from organic pollutants to be effective by the use of modified cyclodextrins it is required a) each time to know the type of the organic compound contained in water that is to be purified, b) each time to prepare the appropriate polymer whose nanocavities will have the appropriate size in order to be able to encapsulate the organic molecules in question. It is therefore obvious that the above disadvantages make difficult water purification. Also the cost of water purification by the application of cyclodextrins is increased, because many different polymeric derivatives must be prepared so as to cover the very large variety of organic pollutants present in water. An additional disadvantage of these modified polymeric cyclodextrins is that they cannot encapsulate large organic pollutants because in any case they cannot have cavities with diameters larger than 11 Å. Consequently, when organic molecules with diameters larger that 11 Å are contained in water, water purification from organic pollutants cannot be effective by the application of cyclodextrin polymers. These pollutants will in every case remain in water, since cyclodextrins cannot have cavities of this size in order to encapsulate these molecules.
An objective of the present invention is to provide modified lipophilic polymers which can encapsulate organic pollutants of a great variety of sizes and shapes and in any case of a greater variety than those that cyclodextrins can encapsulate.
The modified lipophilic dendrimeric and hyperbranched polymers, which are objectives of the present invention are prepared through modification of the functional groups that are located at their surface; the characteristic of these polymers is that the nanocavities that they form are not predetermined. These nanocavities are induced by the size of the pollutants that will be encapsulated, or alternatively they will adjust to the size of these molecules.
Therefore, an advantage of the modified lipophilic dendrimeric and hyperbranched polymers which constitute the object of the present invention is that they can be used for the absorbance/encapsulation of lipophilic pollutants, i.e. molecules of a large variety of sizes and shapes. This is due to the flexibility of the segments of the polymer from the surface of the molecules onwards to the end of the lipophilic chains, and also under the surface of the molecules in question (on the dendrimeric scaffold of the molecules). This flexibility results in the successful encapsulation of a large variety of organic lipophilic pollutants of different kinds and of different shapes in each material (modified lipophilic dendrimeric and hyperbranched polymer) that we prepare and use. Further, it is possible to use the same material for the removal of organic pollutants of a large diversity of sizes and shapes.
In addition, the modified lipophilic dendrimeric and hyperbranched polymers which constitute an object of the present invention can effectively be used for the encapsulation of lipophilic pollutants, the molecules of which may have diameters larger than 11 Å.